1. Field of the Invention
This invention pertains in general to the field of breathing apparatuses having delivery devices for delivery of substances via a gas flow to a patient. More precisely, the invention relates to monitoring the proper function of such delivery devices for safety purposes.
2. Description of the Prior Art
Various delivery devices for substances to be delivered to patients connected to breathing apparatuses are known, such as anesthetic vaporizers for gasifying liquid anesthetic agents. Breathing apparatuses include for instance anesthesia machines, intensive care ventilators with added anesthesia capabilities, etc.
An erroneous function of such delivery devices may involve a safety hazard potentially exposing a connected patient to situations with dire consequences, e.g. when a non-desired amount of the substance should be delivered to the patient.
Hence, there is a need of controlling the correct or desired function of such delivery devices in the breathing apparatuses.
For instance EP-0545567-A1 discloses a method and apparatus for metering to a patient an anesthetic vaporized from anesthetic liquid held in a liquid space of a liquid container into a gas space. The anesthetic dose contained in a gas flow supplied to a patient is determined by the volume/flow of gas passing through the liquid space, i.e. a traditional by-pass vaporizer. The dose is adjusted in a manner that the dosage of anesthetic in a gas intended to be respired by a patient matches a desired dosage and the dosage adjustment of anesthetic contained in a gas supplied to a patient is effected automatically whenever the current dosage differs from a desired value.
However, the apparatus of EP-0545567-A1 needs to determine a desired dosage of anesthetic. Determining a dosage as described in EP-0545567-A1 may be regarded being complicated. Hence there is a need for a simpler system. Further, the apparatus uses either pressure drop based flow meters, or optical sidestream based measurements systems, which are expensive and have further drawbacks.
When using pressure drop flow sensors or heat wire anemometers for measuring gas flow, compensation has to be made for changes in gas composition.
Optical gas analyzers are good but expensive. Moreover, taking a sidestream gas sample from the mainstream involves a time delay for the measurement due to the transportation time from the sample point to the optical gas analyzer; the main gas flow is interfered with by drawing a sample volume, which itself raises issues where to dispose or feedback the sample gas volume after measurement from the optical analyzer; sampling is only based on a small portion of the gas conduit at the sampling point, amongst other disadvantages.
Furthermore the output of sensor units such as a pressure drop based flow meter or a heat wire based flow meter is depended on both the gas flow and physical properties of the measured gas. Particularly in a fault situation, where it is most important to ensure patient safety can both flow and gas concentration be unknown at the same time when using such sensor units. When relying on such sensor units in breathing apparatuses, the system can therefore not distinguish changes in concentrations from changes in flow. Thus, there is a need to provide alternatives avoiding the aforementioned issues and it would for instance be advantageous to be able to measure flow and/or concentration independently.
Hence, an improved or alternative system for determining the presence of a substance delivered into a gas flow would be advantageous.
Hence, an improved breathing apparatus would be advantageous and in particular allowing for increased cost-effectiveness, improved reliability, versatility, and/or patients safety would be advantageous.